Boko Haram, climate change, predatory armies, and extreme hunger are converging on a marginalized population in Central Africa.

Chad was named for a mistake. In the eighteen-hundreds, European explorers arrived at the marshy banks of a vast body of freshwater in Central Africa. Because locals referred to the area as chad, the Europeans called the wetland Lake Chad, and drew it on maps. But chad simply meant “lake” in a local dialect. To the lake’s east, there was a swath of sparsely populated territory—home to several African kingdoms and more than a hundred and fifty ethnic groups. It was mostly desert. In the early nineteen-hundreds, France conquered the area, called it Chad, and declared it part of French Equatorial Africa.

A few years later, a French Army captain described Lake Chad, which was dotted with hundreds of islands, as an ecological wonder and its inhabitants as “dreaded islanders, whose daring flotillas spread terror” along the mainland. “Their audacious robberies gave them the reputation of being terrible warriors,” he wrote. After his expeditions, the islanders were largely ignored. “There was never a connection between the people who live in the islands and the rest of Chad,” Dimouya Souapebe, a government official in the Lake Region, told me.

Moussa Mainakinay was born in 1949 on Bougourmi, a dusty sliver in the lake’s southern basin. Throughout his childhood and teen-age years, he never went hungry. The cows were full of milk. The islands were thick with vegetation. The lake was so deep that he couldn’t swim to the bottom, and there were so many fish that he could grab them with his hands. The lake had given Mainakinay and his ancestors everything—they drank from it, bathed in it, fished in it, and wove mats and baskets and huts from its reeds.

In the seventies, Mainakinay noticed that the lake was receding. There had always been dramatic fluctuations in water level between the rainy and the dry seasons, but now it was clear that the mainland was encroaching. Floating masses of reeds and water lilies began to clog the remaining waterways, making it impossible to navigate old trading routes between the islands.

Lake Chad is the principal life source of the Sahel, a semiarid band that spans the width of Africa and separates the Sahara, in the north, from the savanna, in the south. Around a hundred million people live there. For the next two decades, the entire region was stricken with drought and famine. The rivers feeding into Lake Chad dried up, and the islanders noticed a permanent decline in the size and the number of fish.

Then a plague of tsetse flies descended on the islands. They feasted on the cows, transmitting a disease that made them sickly and infertile, and unable to produce milk. For the first time in Mainakinay’s life, the islanders didn’t have enough to eat. The local medicine man couldn’t make butter, which he would heat up and pour into people’s nostrils as a remedy for common ailments. Now, when the islanders were sick or malnourished, he wrote Quranic verses in charcoal on wooden boards, rinsed God’s words into a cup of lake water, and gave them the cloudy mixture to drink. By the end of the nineties, the lake, once the size of New Jersey, had shrunk by roughly ninety-five per cent, and much of the northern basin was lost to the desert. People started dying of hunger.

In 2003, when Mainakinay was fifty-four years old, he became the chief of Bougourmi. He was proud of his position, but not that proud; his grandfather had presided over more than four hundred islands—until the government stripped the Mainakinays of their authority as Chiefs of the Canton, a position that they had held for more than two hundred years. The center of power was moved to the town of Bol, on the mainland. The islanders were of the Boudouma tribe; the mainlanders were Kanembou. They didn’t get along.

Other political developments were more disruptive. Colonial administrators had drawn the boundaries of Chad, Cameroon, Nigeria, and Niger right through tiny circles of huts on the islands. When these nations enforced their borders, the fishermen and cattle herders of Bougourmi, which is in Chad, were cut off from the lake’s biggest market, which is in Baga, on the Nigerian shoreline. In the mid-aughts, hungry and desperate, they turned to foraging in the bush for fruit and nuts. Then they began to run out of fruit and nuts.

“These were our problems before,” Mainakinay told me, in late July, as he sat on the ground inside a reed hut. He wore a white robe over his bony shoulders, and his dark-brown eyes were turning blue at the edges, fading with age. “It was only recently that our real suffering began.”

One night in 2015, Mainakinay saw flames coming from the huts on Médi Kouta, less than a mile away. For the past several years, Boko Haram had sought to establish a caliphate in northeastern Nigeria. Mainakinay had heard of the group on his shortwave radio. Now, after spreading out along the lake, into southern Niger and northern Cameroon, Boko Haram had come to the Chadian islands and begun kidnapping entire villages, replenishing its military ranks and collecting new wives, children, farmers, and fishermen to sustain its campaigns. At dawn, Mainakinay led the people of Bougourmi to a neighboring island to hide. But Boko Haram continued its attacks, and so, for the first time, Mainakinay’s people sought refuge on the mainland, leaving their cattle and belongings behind.

The jihadis encountered little resistance in Lake Chad. Most islands had no more than a couple of hundred inhabitants, and their machetes and fishing tools were no match for Boko Haram’s grenades and assault rifles. When the militants arrived on Médi Kouta, they set fire to the mosque and beheaded a few men; after that, the terrified islanders followed the fighters into wooden boats and paddled west, to Nigeria and Niger. As they moved farther away from the Chadian side of the lake, the captives noticed that some islands were already flying the jihadis’ black flag.

That spring, a few thousand Boudouma fled to the Chadian mainland, near Bol. The United Nations, anticipating military operations in the islands by Chad against Boko Haram, contacted the government. “We met with the minister of defense and the chief of the Army, and urged them to let us know what they’re planning,” Florent Méhaule, the head of the U.N.’s Office for the Coordination of Humanitarian Affairs in Chad, told me.

Chad is a weak state with a strong military, known for its brutal treatment of combatants and civilians. In late July, without notifying the U.N., the Chadian Army ordered an evacuation of all islands in the southern basin, warning that anyone who was still there in a week would be considered a member of Boko Haram. Around fifty-five thousand islanders rushed to the mainland. The Boudouma have an extensive history of raiding the Kanembou, and the Chief of the Canton did not allow them into the towns. According to Méhaule, “He just told them, ‘Go stay in the empty land between villages. The humanitarians, in their white vans, will come.’ ”

The evacuation of the southern basin took place just before the harvest, so Boko Haram collected whatever millet, wheat, and maize the islanders had left behind. By the end of November, the Chadian Army had swept through the northern basin, forcibly displacing more than a hundred and ten thousand people in total. They ended up scattered among roughly a hundred and forty spontaneous sites across a vast, inhospitable terrain. “People were everywhere—in places we did not know,” Méhaule said. Because Boko Haram had used boats to attack the islands, the Chadian government banned the use of fishing boats, so the Boudouma had virtually nothing to eat. Without sufficient pasture, many of the Boudoumas’ cattle died.

Méhaule and his colleagues set off in convoys of white Toyota Highlanders, searching for the displacement sites. There were no roads or signs, no paths to follow. “All of our maps were wrong, because they were from the nineteen-seventies,” Méhaule told me. “We were driving through areas that should have been underwater, but we couldn’t even see the lake.”

In recent years, the Lake Chad region has become the setting of the world’s most complex humanitarian disaster, devastated by converging scourges of climate change, violent extremism, food insecurity, population explosion, disease, poverty, weak statehood, and corruption.

The battle against Boko Haram spans the borders of four struggling countries. It is being waged by soldiers who answer to separate chains of command and don’t speak the same languages as one another, or as their enemies, or as the civilians, in the least developed and least educated region on earth.

Across the Sahel, millions of people are displaced, and millions more are unable to find work. The desert is expanding; water is becoming more scarce, and so is arable land. According to the U.N., the region’s population, which has doubled in the past few decades, is expected to double again in the next twenty years.

The Sahel is rife with weapons and insurgencies, and some states are beginning to collapse. In recent years, cattle herders and farmers have started killing one another over access to shrinking pastures—the number of deaths exceeds fifteen thousand, rivalling that inflicted by Boko Haram.

Western countries and the United Nations have been trying to stabilize local governments. Since the early aughts, the U.S. has spent hundreds of millions of dollars on strengthening Sahelian security forces, in a bid to limit the spread of jihadism in the region’s vast, ungoverned spaces. But this strategy fails to take into account the complex cruelties of colonialism and the predatory nature of the regimes that have developed in its place. Across the Sahel, many people experience no benefits from statehood, only neglect and violence. “What we are actually doing is making the predator more capable,” a European security official told me. “And that’s just stunningly shortsighted.”

After France took over Chad, it learned that the territory lacked the riches that colonial powers had discovered elsewhere in West and Central Africa. France sent its least experienced and worst-behaved officers there—often as a kind of punishment—and, in the ensuing decades, French military campaigns disrupted trade routes and local economies, contributing to the deaths of hundreds of thousands of people from famine. The French focussed their attention on the forced production of cotton, in a fertile part of southern Chad that they referred to as “le Tchad Utile”—Useful Chad.

In 1958, French Equatorial Africa split up, and two years later Chad became an independent state. The country’s borders had been determined by colonial agreements, and many Chadians couldn’t communicate with one another—there were at least a hundred and twenty indigenous languages. Some Chadians in remote areas were unaware that their villages now belonged to a state.

The country spent the next several decades “suspended between creation and destruction,” as the South African historian Sam Nolutshungu writes, in “Limits of Anarchy: Intervention and State Formation in Chad.” It was “aberrant, marginal, a fictive state,” a country that existed, “even in its peaceful moments, alternately under a cloud of contingent anarchy or tyranny.”

Chad was constantly threatened from the north. Libya’s dictator, Muammar Qaddafi, aimed to form what he called a “Great Islamic State of the Sahel,” and he repeatedly sponsored attempts to topple Chad’s leaders. The French usually supported whichever autocrat or warlord was in power. Chad’s institutions were propped up by French investors and advisers, and hardly extended beyond the capital, N’Djamena. The illusion of Chadian statehood was useful for France and the United States, who saw a strong Chadian Army as a means with which to cripple Qaddafi’s ambitions.

Hissène Habré became President in 1982, in a revolt sponsored by the C.I.A. He had led three violent rebellions and held Europeans hostage, and yet the moment he took the capital he inherited all the international structures of legitimacy afforded to any head of state. Habré ran a vicious security state, with secret detention centers, that tortured and executed tens of thousands of its citizens. But Habré despised Libya’s leader; because of this, the U.S., under Ronald Reagan, supplied him with hundreds of millions of dollars’ worth of weapons. In 1983, Qaddafi invaded northern Chad, using Soviet tanks. In theory, France and the U.S. were no longer backing a warlord. They were helping a President preserve the territorial integrity of his nation.

Habré’s soldiers fought Qaddafi’s forces in a fleet of Toyota Hiluxes supplied by the C.I.A. In what became known as the Toyota War, the Chadian Army killed thousands of Libyan fighters.

In 1987, as Qaddafi withdrew his troops, Reagan invited Habré to the White House and praised his commitment to “building a better life for the Chadian people.” Then Habré resumed slaughtering ethnic minorities who protested his rule. He also accused three of his highest-ranking officials of plotting a military coup. Two of them were captured and killed. The third, a young colonel named Idriss Déby, fled east to Sudan, and recruited others to join him in a rebellion. Déby also went to Libya, where Qaddafi supplied him with cash and weapons. The next year, Déby’s group drove back across the desert. Habré fled into Cameroon, and Déby became the President of Chad.

It was December 2, 1990. To be Chadian was to be born into a territory where you had a fifteen-per-cent chance of dying before your first birthday. In a country of five million, there were five hospitals, and a few dozen qualified doctors. People routinely died of malaria, cholera, and starvation. The average citizen lived to thirty-nine.

Two days later, Déby gave his first public speech. “I have brought you neither gold nor silver but liberty!” he said. “No more military campaigns. No more prisons.” He claimed that he was “determined to lead Chad, with the participation of all its citizens, to the system of government longed for by all: a system of government based on democracy.” He paused. “I mean, democracy in its fullest sense.” It was a telling slip: a new constitution enshrined freedoms of religion, expression, demonstration, and the press, but, in the years that followed, people who tried to exercise those rights often disappeared.

Chad’s economy was nearly nonexistent. Many Chadians—including former and current rebels, soldiers, and police officers—resorted to highway banditry to survive. After Déby told gendarmes that bandits “should be shot down like a dog,” some officials held public mass executions of suspected criminals, without trials. One day in 1996, gendarmes in N’Djamena arrested an elementary-school student who had stolen food from his neighbors. They put a bag over his head, shot him, and abandoned his body on the banks of the Chari River.

Ten days later, Déby met with representatives from several fledgling Chadian human-rights organizations. He told them that the killings were “in accordance with the wishes of public opinion.” Otherwise, Déby has left his citizens in total neglect. The Irish Times reported that, outside the capital, Chadians were eating boiled leaves and animal feed, and digging up anthills to search for whatever grains the insects had dragged home. “This country is a bit of a police state, but mostly a pirate ship,” the European security official told me. “That’s the sense that I get when I’m here—that I’m on a pirate ship, and the captain is always drunk.”

Déby’s security forces used military planes supplied by the U.S. and France, and maintained by American and French technicians, to transport political prisoners. The French also supplied Déby’s regime with money, trucks, fuel, communications systems, and handcuffs—resources that, according to Amnesty International, had been “diverted from their original purpose to be used for execution and torture.” Although French military advisers stationed at Chadian outposts had witnessed human-rights abuses, they did not intervene, saying that it was not their responsibility to come between the state and its people.

Since Déby took power, his forces have put down numerous rebellions and coups. In 2006, Déby and the President of Sudan sponsored insurrections against each other. The Chadian rebels made it all the way to N’Djamena. French soldiers helped stabilize the capital, but near the Sudanese border the Chadian Army forcibly conscripted children. “Déby has trouble finding soldiers who are willing to fight for him,” a senior Chadian military officer told Human Rights Watch. “Child soldiers are ideal, because they don’t complain, they don’t expect to be paid, and, if you tell them to kill, they kill.”

In 2008, Congress passed a law that banned American military support for governments that used child soldiers. But President Barack Obama secured a waiver for Chad, arguing that it was “in the national interest” of the United States to train and equip Chad’s military. Al Qaeda’s message was taking root in parts of Africa where nation-states had been sloppily crafted and poorly ruled. The war on terror had reached the Sahel.

Around that time, Mohammed Yusuf, a young Salafi preacher in northeastern Nigeria, was delivering sermons about the ruinous legacy of colonialism and the corruption of Nigeria’s élites. After decades of political turbulence and military coups, oil extraction had made Nigeria the richest country in Africa, and yet the percentage of people living in total poverty was growing each year. “The Europeans created the situation in which we find ourselves today,” Yusuf said. It was easy to appeal to the existential grievances of northern Nigeria’s marginalized, unemployed youth. Yusuf told them that the only way forward was to install a caliphate in Nigeria. His followers, who became known as Boko Haram, revived a tradition of jihadism in northern Nigeria that goes back hundreds of years.

In the course of his life, Moussa Mainakinay, the chief of Bougourmi, has witnessed drought, plague, and famine in the islands. “It was only recently that our real suffering began,” he said. In 2015, Boko Haram attacked.

Photograph by Paolo Pellegrin / Magnum for The New Yorker

On June 11, 2009, police officers at a checkpoint in Nigeria stopped a group of Boko Haram members on their way to a funeral; in the confrontation that followed, officers opened fire and injured seventeen jihadis. The next month, around sixty Boko Haram members attacked a police station. Gun battles erupted in several towns, and Yusuf was arrested. A few hours later, the police executed him and dumped his body outside the station. A video of the mutilated corpse, still in handcuffs, went viral. Violence exploded all over northern Nigeria: at least seven hundred people were killed in the first week. Yusuf’s deputy, Abubakar Shekau, became the leader of Boko Haram.

Shekau dispatched some of his followers to train with Al Qaeda in the Islamic Maghreb. When they returned, the group detonated car bombs in Nigeria’s capital, Abuja. Propaganda videos show Shekau double-fisting Kalashnikovs and screaming incoherently as he fires bullets into the sky. In 2012, after leading a rampage in the Nigerian city of Kano, he said, “I enjoy killing anyone whom God commands me to kill, the way I enjoy killing chickens and rams.” Shekau’s fighters terrorized remote villages, tossing grenades into huts and burning down mosques. They raped women, slaughtered men, and kidnapped children, whom they forced to carry out suicide bombings. Shekau pledged his group’s allegiance to the Islamic State, but his battlefield tactics were so depraved that ISIS eventually disowned him. Young men who joined Boko Haram were sent back to their villages to recruit their families. As a teen-age fighter explained to me, “If your family doesn’t come, you have to kill them, because they have chosen to be infidels.”

The Nigerian security forces responded with a series of massacres that drove villagers into the insurgency. One day in 2013, after Boko Haram killed a Nigerian soldier near Baga, on the muddy western shores of Lake Chad, government troops stormed into the town, lit thatched huts on fire, and shot villagers as they tried to escape. Some villagers tried to swim to the islands and drowned in the lake. Roughly two hundred people are thought to have died, and more than two thousand structures were burned.

On January 3, 2015, Boko Haram returned to Baga and attacked a local military base. The soldiers shed their uniforms and fled into the bush, leaving behind weapons, vehicles, and ammunition. During the next four days, Boko Haram slaughtered civilians in Baga and the surrounding villages. “It was impossible to know how many people they killed,” a survivor told me. “I just saw bodies in the streets. Everyone was running.” Thousands of people made for the islands of Lake Chad. Boko Haram followed them.

Many islanders were open to Boko Haram. The Boudouma used Nigerian currency, and for decades those who could afford to had been sending their children to study with Quranic tutors in northern Nigeria. A few years ago, some of those children started calling their siblings and friends, urging them to leave the islands and join Boko Haram. “They told me that if I join them I will go to paradise,” a sixteen-year-old Boudouma told me. “They also said that, at their camp in Nigeria, there are buckets full of money, and you can just take as much as you want. So I followed them.”

Dimouya Souapebe, the government official, said that “it was easy for Boko Haram to come in from Nigeria and poison people’s minds,” by promising access to basic services and Islamic education. “The islanders never had a school. They’ve never had sanitation. They drink the same lake water they defecate in. Out in the islands, there is nothing.”

As a first line of defense on the mainland, the Chadian governor of the Lake Region set up “vigilance committees,” with the help of tribal chiefs. Given Chad’s history of rebellion, the governor was wary of allowing vigilantes to carry weapons, but he distributed cell phones to young men so that they could alert the authorities.

On a Tuesday evening in December, 2015, some months after Moussa Mainakinay and his villagers fled Bougourmi, a contact living on a jihadi-controlled island warned him that Boko Haram was planning to attack the market in Bol, the biggest town on the Chadian side of the lake. That night, Mainakinay and a group of vigilantes stood guard, looking for boats. Eventually, they spotted a canoe moving toward them, containing several men and women. When it reached the shore, a few of the passengers detonated suicide vests, killing most of the others. Flesh and cloth rained down. A teen-age girl collapsed screaming; the explosion had mangled her legs.

The vigilantes took her to the hospital in Bol, a small concrete building with rudimentary supplies. Someone roused Sam Koulmini, one of only two doctors in Bol. (The other is his wife.) “Boko Haram told the girl that the explosives wouldn’t hurt her—that, if she killed some people in the market, they’d give her money when she got back,” Koulmini told me. That night, he amputated her right leg and one of her damaged fingers.

For the next several days, she was kept in an isolated room, guarded by gendarmes. During her time with Boko Haram, she had become addicted to tramadol, an opioid painkiller that is widely abused in the region. “A macro-dose of tramadol makes you feel as if you’re in the clouds,” Koulmini explained. “You’re afraid of nothing. Pretty much all the young people are taking it.” The injured girl showed severe symptoms of withdrawal; held in isolation, he says, “she became psychotic.” On the second day, she started smearing feces all over her body.

The gendarmes wouldn’t let Koulmini visit his patient more than once a day, and they rushed him as he changed the dressings on her wounds. By the time he noticed that there were still pieces of shrapnel inside her left leg, it was too late; the limb was gangrenous. He had to cut that leg off, too.

Because Boko Haram had used boats to attack the islands, the Chadian government banned the use of boats. Boudouma fishermen were left with virtually no way to feed their families.

Photograph by Paolo Pellegrin / Magnum for The New Yorker

Before Boko Haram invaded the islands, humanitarian groups in Chad were preoccupied elsewhere, dealing with nationwide health and malnutrition crises, and with refugee crises near Chad’s borders with Sudan and the Central African Republic. “We all had to open very quickly,” Méhaule, of the U.N.’s Office for the Coordination of Humanitarian Affairs, told me. But the Lake Region was so poor and undeveloped that it was hard to distinguish the needs of the displaced islanders from those of mainland villagers. “Some of the displaced, for example, own a huge quantity of cattle,” he said. In the short term, they may be better off than people who have shelter but no food.

In late July, I flew from N’Djamena on an aging propeller plane that, twice a week, takes humanitarians and supplies to Bol. From the sky, I could see black smudges, clustered circles in the sand—remnants of burned-out villages. The movement of people and cows had left faint tracks across the islands and through the reeds and lily pads that filled the waterways between them.

For the next week, I travelled through the Lake Region with two UNICEF employees and the photographer Paolo Pellegrin. The Chadian government was kept informed of our activities and movements; each time we arrived in a different jurisdiction, UNICEF scheduled a “courtesy visit” with the local authorities, and gave them copies of our papers and photographs.

There are no roads in the region, so we followed in the tracks of vehicles belonging to the military and to other N.G.O.s—up sandy hills, past millet patches and goat pens made of gnarled roots and thorny vines. The pens rarely had any goats in them. We rattled downhill into flat, dark-brown depressions that, until recently, had been part of the lake bed. There, people were digging for natron, a mineral ash that’s put into camel feed; the going rate for a hundred-pound bag of natron is less than three dollars. According to Méhaule, the soil left by the lake’s receding waters is so rich that, properly farmed, it could grow enough food to sustain everyone who’s currently starving next to it. But the Chief of the Canton has refused to give displaced Boudouma access to arable plots.

As we drove, we would suddenly come across a reed hut. Then another would come into view, then a hundred more—each big enough for three or four people to lie down in. We would pass a metal billboard announcing the name of the displacement site, as well as the organizations and the countries who were funding some of its needs. Here was the UNICEF-backed well. Over there was the Oxfam one, where children were using their full weight to pull down the lever. Then there was the sign announcing a “joint education project,” paid for by Handicap International, Cooperazione Internazionale, and the Swiss Confederation—although we saw no schools. In certain ways, the displacement sites offer an improvement over life in the islands. Every so often, representatives of international organizations arrive to vaccinate the cows; build a well; talk to the women about health issues; and weigh the children and measure their upper arms, to calculate the level of malnutrition. At one site, I met a woman whose hands had been blown off when Boko Haram threw a grenade into her hut. She had been nine months pregnant, with her seventh child, but after the attack she miscarried. When her husband saw her condition, he left her, sold their last cow, and remarried within two weeks. Having fled the islands, she is now regularly visited by a mental-health professional.

Still, on the Chadian side of the lake, it is better to be any nationality but Chadian. Just outside Baga Sola, the second-largest town in the Lake Region, there is a camp for displaced Nigerians. Around five thousand people live there, most of whom fled the massacre in Baga, across the lake. Because they crossed an international border, they have refugee status, which makes them eligible for funding and legal protections that are not available to the internally displaced. The Nigerian camp has a school with large classrooms, blackboards, chalk, and wooden desks. There’s an outdoor basketball court, with floodlights; indoor latrines are a short walk away. Police officers patrol the camp, which is divided into sixteen neatly spaced blocks of roomy, waterproof tents. “The security is good here, and we have enough food,” a teen-age girl told me. “I am getting an education for the first time. Why would I want to go back to Nigeria?”

No such amenities exist in the sites for internally displaced Chadians, or even in the Kanembou villages. One morning, a heavy rainstorm flooded Baga Sola. Goats huddled against a mud wall to avoid the wind. When the storm lifted, I went to the Kafia displacement site, which is home to a few thousand Boudouma. Everyone was soaked. Several reed huts had collapsed; their remnants were strewn across a desolate, sandy landscape. A camel gnawed at a prickly tree. “We eat one meal per day, at most,” a Boudouma chief told me. “Often we eat nothing.”

After Boko Haram attacked Baga, each country bordering the lake supplied a couple of thousand soldiers to an effort called the Multi-National Joint Task Force, which receives intelligence from Western partners. But coöperation among the countries is fragile. One day, at the task-force base in N’Djamena, I met the commander, a wiry, deadly serious Nigerian major general named Leo Irabor. He sat at an imposing desk, with a wall of maps behind him. I told him that I hoped to embed with his troops and to travel north of the lake, west through the desert into Niger, and then south into Nigeria. “It is a fine idea,” Irabor said. “But it is not possible,” because the M.N.J.T.F. doesn’t conduct cross-border operations. The military sectors are divided along national boundaries, and the countries have a history of mistrust—especially between the government of anglophone Nigeria and those of the other countries, which are francophone. Soldiers can pursue militants across borders, if necessary, but only Boko Haram fights as if the borders don’t exist. “None of the partner countries want to end up shouldering most of the burden,” a Western military adviser to the M.N.J.T.F. told me, with a shrug. “We can’t want it to work more than they do.”

The M.N.J.T.F. doesn’t fight for new ground in the islands during the rainy season—the weather can damage vehicles and leave fighters stranded—but, in the past two dry seasons, it has taken significant territory back from Boko Haram, spurring defections. Last year, on August 25th, seven Boudouma men and one woman showed up at an M.N.J.T.F. checkpoint in Chad, near the border with Nigeria. For more than a year, they had been living with Boko Haram; now they wanted to come home. By the end of 2016, around three hundred men and seven hundred women and children had returned. They were kept in military detention in Baga Sola while the government figured out what to do with them.

Eventually, all the women and children were let go, and it fell to the U.N. to reunite them with other people from their villages among the scattered displacement sites. “There was a big risk that they wouldn’t be welcome—that they would be stigmatized or retaliated against,” Méhaule, of OCHA, said. “But the reintegration was surprisingly easy.”

Many islanders have sought refuge in displacement sites on the mainland. “Often we eat nothing,” one chief said.

Photograph by Paolo Pellegrin / Magnum for The New Yorker

One afternoon, at the Mélea displacement site, near Bol, I met a twelve-year-old boy whom I’ll call Aboudou. He looked about half his age. He wore ragged green pants, a filthy shirt, and, despite the scorching temperatures, a yellow woollen hat, which he pulled down over his eyes whenever he started to cry. His face was marked with the traditional scarification of the Boudouma—a deep cut down the center of the nose, and diagonal marks on each cheek—and his skin was so taut that you could see his jaw muscles move when he spoke.

Aboudou, his parents, and his four younger siblings had been kidnapped by Boko Haram, during the attack on Médi Kouta, near Bougourmi. The family had canoed with the jihadis for two weeks, until they reached the island of Boka, in southern Niger, where his mother and father built a house out of red water lilies. Each day, Aboudou and several hundred other children were given religious lessons by a man named Mal Moussa, who, Aboudou said, taught them that “if you kill an infidel, you will go to paradise.”

Life on Boka was hard. Sometimes Aboudou’s mother would try to talk to him about the abduction, but if someone else came near she quickly changed the subject. Most nights, his father disappeared, and he didn’t know why. People who disobeyed orders were beheaded. Eventually, the island ran out of food, and they moved to another one, to harvest maize.

One day, airplanes came and bombed all the huts. A piece of shrapnel pierced Aboudou’s shoulder. He had fifteen friends on the island, but when the attack was over all of them were dead. After that, his family fled to Chad, where they were detained by the military. He was much more afraid of the uniformed soldiers than he was of Boko Haram.

Aboudou’s mother confirmed his account. When I asked whether her husband had participated in jihadi raids on the nights he disappeared, she said she didn’t know. “He never told me what he did, and I never asked,” she said. When I asked to speak with him, she said that it was impossible—he was on his way to the market. But he had brought Aboudou to me a few hours earlier, and now I saw him, about fifty feet away, staring at us from his hut.

The Chadian military didn’t know what to do with the returning men. Many of them had received weapons training from Boko Haram, and some had carried out attacks. Méhaule advised the government to screen them, identify and prosecute perpetrators of crimes, and let the others go. “But the government had no capacity to do this,” he told me. “It’s expensive to feed three hundred people, so, in January, they just released them. All of them.”

This year, several hundred more people have returned. “Those who had left to join Boko Haram learned that the humanitarian community is here, giving people food to eat, giving people money,” Souapebe, the government official, told me. “That’s why people started coming back.” To encourage further defections, he said, “I buy phone credit for the local boys. Then they call their friends in Boko Haram and tell them, ‘We’re O.K. We have food. We have shelter. The humanitarians have given us blankets.’ ” He continued, “When someone is no longer hungry, he is no longer dangerous.”

One of the boys who had voluntarily joined Boko Haram came back to Chad because, he told me, “Boko Haram lied to us about the money. All I saw was poverty and death.”

On the morning of July 22nd, we set off by boat in the direction of Médi Kouta. The chief of the island, a seventy-two-year-old Boudouma named Hassan Mbomi, met us at the shoreline and guided us uphill, through a grove of charred palm trees. He had returned to the island twenty days earlier, to try to grow millet, because he was starving on the mainland. About two hundred people had followed him. “When we got back, everything was burned,” he said. “We have to build our village from scratch.” A large group of men were waiting for us in a dusty clearing, but Mbomi said I couldn’t speak to them. He said that they had been kidnapped by Boko Haram and forcibly conscripted into the jihad before escaping.

The lake used to give the islanders everything: they ate from it, drank from it, and built houses from its reeds.

Photograph by Paolo Pellegrin / Magnum for The New Yorker

To comply with U.N. safety rules, we were accompanied into the islands by a Chadian soldier named Suliman. He seemed ill at ease on Médi Kouta, and the people there eyed him with suspicion. When we left the island, Suliman told me that he didn’t accept the chief’s explanation. “Sometimes they go away, sometimes they come back,” he said. “But they are all complicit.” Some jihadis have a branding on their back—a circle with a diagonal line through it—but, in most cases, “we can’t distinguish who is Boko Haram and who isn’t,” Suliman said.

For two years, Suliman had been fighting in the islands. The Army had no boats. Sometimes his group commandeered fishermen’s pirogues, and he had come to believe that many fishermen worked as spies, alerting Boko Haram to the military’s movements. Like most soldiers, he grew up speaking Chadian Arabic, and cannot communicate with people in the Lake Region. We passed another island lined with burned palm trees. “The jihadis used to come to these islands at night, and we couldn’t see them,” Suliman said. “So we would light the trees on fire, so they wouldn’t come back.” He had torched the trees on Médi Kouta.

While I was in Baga Sola, six thousand people showed up near the Dar Nahim displacement site, a few miles from town. They belonged to a nomadic Arab community that has been in Chadian territory for hundreds of years, but they had just come from Niger, where some of them had fled during the Habré regime. Ordinarily, humanitarian workers would classify them as Chadian “returnees.” But national governments get the final word on status, and Déby’s regime insisted that they were Nigérien refugees, deflecting responsibility and costs to the U.N.

Because governments can decide where the U.N. operates within their national territory, humanitarians are routinely compelled to enter into morally fraught arrangements. In Syria, the U.N. is almost never allowed to deliver food or medicine to besieged civilians who oppose the regime. In Ethiopia, the government has spent the past several decades pressuring N.G.O.s into complying with its coverups of epidemics and a possible famine. In Chad, the International Committee of the Red Cross is the only international organization that has access to prisons. In order to maintain access, the I.C.R.C. keeps any atrocities it sees confidential.

But more common is the scenario in Lake Chad—in a neglected patch of territory, the international community ends up fulfilling the unwanted obligations of statehood. The regime reaps the benefit: the threats that arise from its failure to govern are mitigated, and its leader is left to focus on the task of strengthening the security apparatus that keeps him in power. As Linda Polman writes, in “The Crisis Caravan,” from 2010, “If you use enough violence, aid will arrive, and if you use even more violence even more aid will arrive.”

Once a humanitarian emergency has been stabilized, it is usually followed by extensive development projects, funded by international donors and institutions. “Baga Sola is three times bigger than it was when we all moved in,” Méhaule said. “It’s amazing how the money flowing in from humanitarian assistance has changed the city.” Jihadi activity in areas susceptible to recruitment tends to attract the major Western donor countries, who see development as an instrument of stabilization. But, if Boko Haram were to suddenly disappear, the humanitarian emergency funds would be directed to other crises, in other desperate parts of the world. The people of the lake would be no less vulnerable to environmental degradation and all its consequences, but, as before, they would largely be on their own. Travelling through the Lake Region, I got the impression that almost everyone there—and especially those in the Presidential palace—has a stake in Boko Haram’s continued existence as a distant, manageable threat.

Even so, the assistance has fallen short of the need. This year, the U.N. appealed for a hundred and twenty-one million dollars in aid for the Chadian side of the lake, but only a third of that has appeared. In the northern basin, I met a twenty-seven-year-old man who, three days earlier, had become so hungry that he walked six hours into contested territory in search of fish. Fifteen other men had gone with him; all of them were captured or killed by Boko Haram.

This past spring, Boudouma men started heading back to the islands in the southern basin, to plant millet and maize before the rainy season. Méhaule’s team followed them. For two years, the Chadian Army had been telling the U.N. that the islands were empty and off limits, but now, he said, “we realized that there were about forty thousand people living there.”

When Moussa Mainakinay, the chief of Bougourmi, went home, he could tell that the lake had receded several hundred feet since he left. There were more reeds and water lilies, and more mosquitoes. The lake water was so shallow and full of sediment that drinking it gave him a stomach ache. Boko Haram had taken the cows and the cooking pots, and either the jihadis or the military had burned all the huts. There was nothing left. But, on the mainland, many from Bougourmi had died of malnutrition, and Mainakinay was determined to bring the remaining people home.

After a few months, a community worker from Bougourmi named Bokoï Saleh arranged for a vaccine delivery to the island. The vaccines would inoculate children against measles, tetanus, polio, and tuberculosis. Unicef paid for the transport logistics.

Saleh picked up the vaccines at the hospital in Bol and, with the help of a friend, hauled them into a pirogue. The load weighed more than six hundred pounds, split among several large coolers. The two men rowed the pirogue from the mainland to a nearby island called Yga, where they borrowed five donkeys to transport the vaccines to the other side of the island. The walk took forty minutes. At the shoreline, there were two hippopotamuses, making it too dangerous to leave. They spent the night there, sleeping on the ground.

This year, hundreds of Boudouma people who were living with Boko Haram have returned to Chad. They now live in temporary displacement sites. One boy who had voluntarily joined the group said, “All I saw was poverty and death.”

Photograph by Paolo Pellegrin / Magnum for The New Yorker

Saleh got up at five o’clock in the morning. It was hot and humid, and he was worried that the coolers might not keep the vaccines fresh for much longer. The hippos were gone, but, during the night, a floating island of reeds and water lilies had blocked the area around his boat. Saleh and his friend started hacking through the reeds with machetes. But they were too thick, so the men abandoned the boat and started dragging the coolers across the top of the floating island. It took half an hour to go a couple of hundred feet, and they had to keep moving to prevent the vaccines from sinking. When they reached the other side, the water was up to their waists. They waved over another pirogue, loaded up the vaccines, and paddled the rest of the way to Bougourmi.

Saleh relayed this story to me later that day, outside a hut on Bougourmi. He was drooping with exhaustion. A few feet away, the vaccination campaign was in progress. At least a hundred women and children were sitting in the shade under the island’s biggest tree, waiting their turn.

I asked the translator to tell Saleh that I admired what he had done. Saleh frowned. “If UNICEF had rented me a pirogue with a motor, I could have avoided the hippos and the reeds,” he said. “It would have taken twenty minutes to get here from the mainland.”

He was right. That’s how UNICEF had brought me.

In N’Djamena, I came to know a Chadian spy who is close to the President. He sought me out, wanting to confide state secrets; I was nervous that it was a trap. But, at our third meeting, he described the structure of a group of military-intelligence agents whose job it is to spy not for the military but on the military—to look out for anyone plotting a coup. “Things are not good here,” he said. “The soldiers are unhappy.”

Déby’s hold on power is reliant on Western support. The European security official told me that “Déby basically blackmails us, saying, ‘If I fall, there’s a direct line between ISIS in the north, Boko Haram in the south, and Al Qaeda in the west.’ ” In a bid to prove his worth to international backers, Déby has been renting out the Army to international coalitions, sending Chadians to fight with U.N. forces in Mali and the Central African Republic. But many of those soldiers have not been paid.

The Chadian economy has become so bad that, in the past year, Déby has repeatedly cut civil servants’ salaries. This summer, he also cut the salaries of his troops, a move that was quickly followed by a carjacking and a spate of armed robberies and shootings in N’Djamena; one humanitarian worker’s stolen handbag turned up on the M.N.J.T.F. base. Chadian infantrymen are now being paid around fifty-eight dollars a month. “The Chadian people are starving for food and for freedom,” the spy said. “I work for the President, but my loyalty is to the Chadian people.”

August 11th was Chad’s fifty-seventh Independence Day, and there was a military parade in the Place de la Nation, a vast public square that rarely has any people in it. Déby didn’t show up until three hours after the festivities began. The next time I met up with the Chadian spy, he said that Déby’s military-intelligence officers had inspected every weapon on display before the President’s arrival, to make sure that none of the guns had secretly been loaded.

Since the country’s independence, the French government has routinely sponsored Chadian military officers to train or study in France—including Déby, during the Habré era. Officially, the purpose of the training has been to help professionalize the Army. But it also seems like a kind of insurance policy, a guarantee that whichever officer leads the next successful rebellion will also have some loyalty to France. In recent months, Chadian rebels linked to Déby’s nephew, Timane Erdimi—who led a failed rebellion in 2008, and has been living in exile ever since—have been massing near the Libyan border. “Everyone dreams of being the President,” the spy told me. “I am just biding my time.”

On most mornings in N’Djamena, French fighter jets roar out of the international airport, to bomb Al Qaeda militants in Mali. The United States has special-operations forces in most Sahelian states, including Chad. The crises of the Sahel have “so many variables that, even in the short term, we don’t have a handle on things,” an American military officer told me.

In recent months, I have asked many American diplomatic and military officials to define a coherent long-term strategy for the region, but none of them have been able to articulate more than a vague wish: that by improving local governments and institutions, encouraging democratic tendencies, and facilitating development, the international community can defeat terrorism. In Chad, the security-based approach mistakes the strengthening of Déby’s regime for the stabilization of the Chadian state. The strategy is a paradox: in pursuing stability, it strengthens the autocrat, but, in strengthening the autocrat, it enables him to further abuse his position, exacerbating the conditions that lead people to take up arms.

As part of international antiterror partnerships, security forces are increasingly coming into contact with communities of people who cross international borders every day. Many who fall into this category are nomadic herders; their way of life is fundamentally at odds with the enforcement of legal boundaries, and they are indifferent to the existence of nation-states. If they are denied the freedom to move with the seasons, their cattle will die. In recent years, as the Sahelian climate has worsened, many herders who had bought weapons to protect their animals have turned to jihad.

It seems likely that, even if Boko Haram is defeated, the rationales for insurgent violence will broaden beyond religion. I asked the European security official whether he thought that, in the future, there will be terrorist groups in the Sahel that carry out attacks in the name of equality instead of jihad. He smiled, and said, “If you examine the lacquer on a wooden table—I think your question is, how thin is that lacquer?”

“Yes.”

“I think it’s pretty thin.” ♦

This article appears in the print edition of the December 4, 2017, issue, with the headline “The Emergency.”